Slight confusion over party sizes

Me and some of my friends GT: Tempist fox3, Legendairy and 2 guest players typically end up 4 player split screening on a Friday or a Saturday. Lately we have been playing halo reach online and we’re somewhat confused as to why the multi-team playlist (3v3v3v3) allows 4 player local party meaning the 4th player ends up on one of the other teams. but both Big team and Invasion 8v8 and 6v6 player play-lists respectively only allow a max local party of 2. Meaning we can’t play them. If i’m being honest i can’t see any advantage to 4 player split screening in either of these modes so I pose the question why doesn’t the system allow it?

Many thanks.

no idea, i think it has to do with connection, and quitting.

Not sure why with BTB but Invasion I think it’s to do with only having one spawn partner on your team and only being able to see that person on your HUD. For example if you were playing 4 player splitscreen on invasion you would have an advantage over everyone else because you could just look at where your teammates are on there part of the screen as well a your spawn partner.

It might be to do with the size of the maps and screen lag as well but that is just me guessing